Kieran Loveridge, convicted of the one-punch killing of teenager Thomas Kelly in Sydney's King Cross, is transferred to a maximum security prison after an alleged improper relationship with a female guard.

One of Sydney's most high-profile legal brothels has denied allegations that illegal drugs are being sold on the premises.

The denials come in the wake of a Four Corners/Fairfax investigation into the behaviour of deregistered neurosurgeon Suresh Nair, who spent thousands of dollars on cocaine and prostitutes while visiting brothels.

Four Corners has interviewed two sex workers who allege they were expected to take drugs with clients at The Golden Apple, and that the drugs were supplied as a "party package" by the brothel.

Dr Nair was jailed after two sex workers died from cocaine overdoses as a result of separate bookings with the surgeon in February and November 2009.

The jail sentence imposed for the one-hit killing of teenager Thomas Kelly is not long enough to act as a deterrent, a Sydney court has heard.

The Court Of Criminal Appeal is hearing an appeal by the Director of Public Prosecutions (DPP) against the minimum four-year sentence given to Kieran Loveridge for punching Mr Kelly in the head in Kings Cross.

The DPP has told the court Loveridge displayed a sustained level of criminality the night he hit Mr Kelly and also assaulted a number of other people.